The present invention relates to a wireless apparatus and mre particularly to a wireless apparatus with freequency synthesizers.
Conventionally, a simple wireless communication system comprises a transmitter and a receiver having the same frequency as the transmitter for receiving the transmitted signals from the transmitter. For example, in a wireless mouse application, a signal is transmitted once the user clicks on the mouse. Then a receiver on the computer receives the same. Finally, the central processing unit (CPU) of the computer processes the received signal accordingly.
It is known that only a signal with fixed frequency is generated in a typical wireless transmitter by either the oscillation of an L/C circuit or the oscillation of an oscillating crystal. Such a single frequency signal is susceptible to unauthorized copying. Thus, it is impossible to provide a safe wireless communication environment to the user by such a typical wireless transmitter. This may cause a loss to the user. An improvement over the above design is to install a number of L/C circuits or oscillating crystals in the wireless transmitter for generating a number of signals with different frequencies.
But this is unsatisfactory for the purpose for which the invention is concerned for the following reason. It increases the size of the wireless transmitter. Inevitably, the size of mouse will also increase. This contradicts the compactness of a typical mouse. Also, there is little space available for the accommodation of such added circuits. In view of this, such technique is impractical.
It is an object of the present invention to provide a wireless apparatus comprising a transmitter and a receiver wherein each of the transmitter and the receiver includes a phase-locked loop (PLL) having a frequency synthesizer for generating a plurality of signals with identifications. Operating signals are combined with said plurality of signals to form said spread spectrum modulated signals prior to transmitting from the transmitter. Correspondingly, the received signals in the receiver are converted into the original signals by the frequency synthesizer in the receiver. With this, it is impossible for an unauthorized party to copy such signals, thereby providing a safe wireless communication environment to the use.